Electronic mail, commonly called email or e-mail, allows a sender to convey a message to one or more recipients over a network (such as the Internet). Email is generated and retrieved using an email client. An email server accepts, forwards, delivers and stores messages. By using a store and forward model, neither the sender nor the recipient is required to be online simultaneously.
An email message consists of three components, the message envelope, the message header, and the message body. The message header contains control information, including, minimally, an originator's email address and one or more recipient addresses. Usually descriptive information is also added, such as a subject header field and a message submission date/time stamp.
Messages are exchanged between hosts using the Simple Mail Transfer Protocol with software programs called mail transfer agents (MTAs); and delivered to a mail store by programs called mail delivery agents (MDAs, also sometimes called local delivery agents, LDAs). Users can retrieve their messages from servers using standard protocols such as POP or IMAP, or, as is more likely in a large corporate environment, with a proprietary protocol specific to Novell Groupwise, Lotus Notes or Microsoft Exchange Servers. Webmail interfaces allow users to access their mail with any standard web browser, from any computer, rather than relying on an email client. Programs used by users for retrieving, reading, and managing email are called mail user agents (MUAs).
Mail may be stored on the client, on the server side, or in both places. When IMAP is used, the messages reside on a server that is remote from the user's computer. IMAP does not actually move messages onto the local computer. When using POP, an email client checks the POP server for new messages and downloads all the new messages in an inbox supported by the client. Typically, a POP client will delete downloaded messages from the server.
Email clients are no longer limited to desktop computers. Tablets, smartphones and other portable devices can connect to an email server and alert a user that new messages are available. In this environment, users are “tethered” to an email server. While this keeps a user connected, it also disrupts private lives, interrupts social activities and draws the user into preparing a response.